Gallinacins: cysteine‐rich antimicrobial peptides of chicken leukocytes

Abstract

We purified three homologous antimicrobial peptides (‘gallinacins’) from chicken leukocytes, examined their antimicrobial activity in vitro, and established their primary sequences by a combination of gas phase microsequencing and on‐line LC‐ESI‐MS analysis of endo‐ and exoprotease peptide digests. The peptides contained 36–39 amino acid residues, were relatively cationic due to their numerous lysine and arginine residues, and each contained 3 intramolecular cystine disulfide bonds. Gallinacins showed primary sequence homology to the recently delineated β‐defensin family, heretofore found only in the respiratory epithelial cells and neutrophils of cattle, suggesting that β‐defensins originated at least 250 million years ago, before avian and mammalian lineages diverged. The 9 invariant residues (6 cysteines, 2 glycines and 1 proline) common to avian gallinacins and bovine β‐defensins are likely to constitute the essential primary structural motif of this ancient family of host‐defense peptides.